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Stopping Toronto’s next flood

Leland Wilbur, operator of Toronto’s G. Ross Lord Dam, can see his house through the control room window overlooking the massive structure and the reservoir it holds back.

Leland Wilbur, a dam operator, at the control panel for the G. Ross Lord Dam near Dufferin and Finch Sts. His house is close to his work, just off to the left, so he can respons to flooding threats at all hours. (Andrew Lahodynskyj / Toronto Star)

The home sits just off to the left — on the lip of the reservoir’s slope. And during storms and spring melts, the lake’s waters, fed by the Don River, can creep menacingly up his expansive back lawn.

Wilbur, who is required to live at that house near Finch Ave. W. and Dufferin St., can be called out at all hours to respond to flooding threats on the river.

Has he been roused from his sleep often? “Oh, yes, definitely,” he laughs.

This rapid-response capacity is crucial in the GTA, whose nine ravine-lined watersheds need little coaxing to overrun their banks.

“Toronto is a very ‘flashy’ city,” says Sameer Dhalla, associate director in charge of restoration and infrastructure with the Toronto and Region Conservation Authority, referring to the risk of flash floods.

“When it rains, it’s instant — water just gets in and rises quickly. We have hours (until the flood hits) if we’re lucky,” he says, adding there are 42 historic communities built on flood plains across the region.

And Dhalla is far from sanguine about the GTA’s ability to control flooding.

“Right now I’d say that we are trending up, but I’d say we’re at a failing grade.”

Toronto and Region Conservation Authority flood control expert Sameer Dhalla at the G. Ross Lord Dam. Dhalla says there is a lot of work to be done to keep the city safe from flooding. (Andrew Lahodynskyj/Toronto Star)

Just how vulnerable the area is to dangerous dousings was made clear on July 8, 2013. A violent storm dumped 126 millimetres of rain on the city, submerging basements, roads and GO train lines, knocking out power and leaving an estimated $850-million mess.

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Many cities, including flood-prone Calgary and Winnipeg, sit on large rivers, whose carrying capacities are five or more times greater than any single GTA waterway, Dhalla says. The sheer volume of water that rivers like the Bow and Red can convey means that floods typically build slowly and call out their intentions.

Calgary in 2013 had three days’ warning, Dhalla says. “They could see them developing upstream.”

But here, heavy thunderstorms — which may become more common and intense with climate change — can overwhelm rivers like the Humber in the west of the city, the Don in the east or the Rouge further east, in hours or minutes.

That was the case on Oct. 15, 1954, when Hurricane Hazel began a 12-hour onslaught, dumping up to 285 millimetres of rain on the area. That storm sent rivers here, especially the Humber, raging over their banks, killing more than 80 people and sweeping away homes, roads and bridges.

But Hazel also swept in the first serious flood control efforts in the region — efforts Dhalla’s authority works closely with local municipalities to co-ordinate. That storm “really changed the face of flood management in Ontario,” he says.

Across the province, 36 conservation authorities now operate. The Toronto and Region Conservation Authority (TRCA) is working with the city of Toronto on its emerging ravine strategy, presented in draft form in June. The TRCA’s recommendations on flood control and conservation will play a key role in the strategy.

It’s clear those recommendations will differ from the post-Hazel playbook.

In the years after that storm, the authority went on a building boom, constructing four dams as part of a $22-million flood control plan. Two are large, manned operations: the G. Ross Lord on the Don and the Claireville on the Humber. (The TRCA owns a total of 11 dams, including ones built for recreational purposes and legacy dams it acquired.)

Leland Wilbur at the G. Ross Lord says his dam can hold back 5.5 million cubic metres of water, protecting low-lying communities. That amount would fill 2,200 Olympic swimming pools. During heavy rains or melts, the reservoir can rise five metres in a matter of hours behind the dam gates, which will release the pooled water slowly as the upstream surge subsides.

The Toronto authority also constructed 23 other flood control structures that include dikes, berms and water diversion channels in the post-Hazel decades.

While all these are useful, Dhalla admits many would not have been built today. For one thing, he says, they can be blights on the natural environment. For another, the natural environment can often provide more robust flood control than man-made structures.

Naturalizing the mouth of the Don River, for example, will alleviate the sporadic flooding that can leave the Don Valley Parkway submerged at its southern end.

This naturalization would take the river straight out into Lake Ontario — past the man-made Keating Channel, where it currently turns 90 degrees before emptying. The TRCA is working with Waterfront Toronto on the project.

“Rather than holding and impounding water, we’re going back to natural systems, where we’re making room for the flood,” Dhalla says.

“We’re opening it up … so we can convey more water and protect the area from flooding.”

Similar naturalization projects are planned to reconfigure rivers in the Vaughan and Brampton city centres.

And across suburbs north of Toronto, the authority has forbidden development on sensitive areas and flood plains, leaving ribbons of green beside many rivers and streams.

Running a flood warning system is also a big part of the mandate, Dhalla says. “We have staff that are on call seven days a week, 365 days a year, (to) monitor conditions.”

The TRCA’s flood monitoring combines streams of data from Environment Canada with a series of 125 rain- and stream-gauging stations across the region. Some 25 of these are equipped to send out real-time data on changes in water levels.

The authority’s operating budget for water risk management was around $670,000 last year, while it spent nearly $27 million in capital endeavours.

Dhalla says long-established centres like areas of the old city of Toronto are particularly vulnerable because tightly compacted infrastructure long made large-scale control measures such as diversion channels and bans on flood-plain development impractical.

“We’re still repairing the erosion from the July (2013) storm event,” Dhalla says.

“So much was lost. People … lost their backyards; houses were at risk of falling in. People were 20 metres away from the river.”

Compounding the risk in dense urban areas is the ubiquitous pavement, which prevents the natural absorption of water into the earth and plants and sends heavy rains, dirtied with pollutants, directly into streams and overburdened storm sewers.

“I’d say over 70 per cent of the urban area in our jurisdiction doesn’t have adequate stormwater controls,” Dhalla says.

Solutions

Heavily urbanized areas do not mix well with rivers and streams. Often built before effective storm management strategies were established, cities dipped down dangerously into flood plains and laid out roadways and parking lots that sent rainwater and melt water rushing into the channels.

“So every single opportunity you can take (to retrofit) highly urban areas you have to,” says Sameer Dhalla of the Toronto and Region Conservation Authority. The associate director in charge of restoration and infrastructure proposes a variety of measures to prevent flooding in the area. They range from simple steps that homeowners or businesses can take such as putting in green roofs to steps involving the TRCA or local governments.

Stormwater Ponds

These take water through collection pipes from urban areas during heavy rains, hold it, and release it slowly into rivers or lakes. The ponds also allow pollutants picked up from pavement to settle as sediments, cleaning the water before it enters the natural system. One such pond was built in North York’s Earl Bales Park.

Green Roofs

The plants and grasses that adorn these rooftop gardens are water absorption machines. They take it up through their roots, use it for photosynthesis and evaporate it back into the air through their leaves in a process known as transpiration. A Toronto bylaw mandates green roofs on many new buildings.

Bioswales

These planted, channelled gullies can be built around parking lots and other paved surfaces where they collect water runoff and use it to feed the foliage. Toronto will be installing these along some rebuilt streets and roadways in the future. Examples are on Bay St. between Grosvenor St. and Wellesley St.

Rain Barrels

Barrels and cisterns placed at homes and businesses collect rain runoff from eaves systems, which owners can then use to water their lawns and plants during dry spells.

Rain Gardens

These are planted in depressions, with foliage that is tolerant of the contaminants in runoff water. The loose soil beneath retains rain longer and filters the water not used by the plants on top. The plants can be fed by eavestrough systems or planted in areas adjacent to high-runoff surfaces.

Permeable Pavement

Permeable pavement may be the most groundbreaking of retrofit proposals. The multilayered system drinks in rainwater and cleans it of the metal-bearing sediments and petroleum pollutants, says Andrea Bradford, a water engineering expert at the University of Guelph.

Most current versions of these products could be used now on parking lots, driveways, shoulders, residential streets or sidewalks, but not on heavily trafficked roads, Bradford says. The cement is being tested now in Mississauga and in the U.S.

On top, the pavements can have familiar interlocking blocks that allow water through the cracks. New permeable concretes and asphalts are being rolled out that contain little if any of the small sandy aggregates, known as fines, abundant in normal mixtures, says Bradford. This leaves gaps between the larger pieces of gravel that allow water to pass through

A thin layer of smaller gravel acts as a smooth bedding for the asphalt or concrete above

A base of larger rock aggregates acts as a reservoir, storing water until it can seep into the ground below. The lower levels of aggregates act as filters for the water as it passes into the earth below and groundwater system. They offer vast storage basins in heavy rains, keeping water away from streams and rivers.

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That was the case on Oct. 15, 1954, when Hurricane Hazel began a 12-hour onslaught, dumping up to 285 millimetres of rain on the area. That storm sent rivers here, especially the Humber, raging over their banks, killing more than 80 people and sweeping away homes, roads and bridges.

But Hazel also swept in the first serious flood control efforts in the region — efforts Dhalla’s authority works closely with local municipalities to co-ordinate. That storm “really changed the face of flood management in Ontario,” he says.

Across the province, 36 conservation authorities now operate. The Toronto and Region Conservation Authority (TRCA) is working with the city of Toronto on its emerging ravine strategy, presented in draft form in June. The TRCA’s recommendations on flood control and conservation will play a key role in the strategy.

It’s clear those recommendations will differ from the post-Hazel playbook.

In the years after that storm, the authority went on a building boom, constructing four dams as part of a $22-million flood control plan. Two are large, manned operations: the G. Ross Lord on the Don and the Claireville on the Humber. (The TRCA owns a total of 11 dams, including ones built for recreational purposes and legacy dams it acquired.)

Leland Wilbur at the G. Ross Lord says his dam can hold back 5.5 million cubic metres of water, protecting low-lying communities. That amount would fill 2,200 Olympic swimming pools. During heavy rains or melts, the reservoir can rise five metres in a matter of hours behind the dam gates, which will release the pooled water slowly as the upstream surge subsides.

The Toronto authority also constructed 23 other flood control structures that include dikes, berms and water diversion channels in the post-Hazel decades.

While all these are useful, Dhalla admits many would not have been built today. For one thing, he says, they can be blights on the natural environment. For another, the natural environment can often provide more robust flood control than man-made structures.

Naturalizing the mouth of the Don River, for example, will alleviate the sporadic flooding that can leave the Don Valley Parkway submerged at its southern end.

This naturalization would take the river straight out into Lake Ontario — past the man-made Keating Channel, where it currently turns 90 degrees before emptying. The TRCA is working with Waterfront Toronto on the project.

“Rather than holding and impounding water, we’re going back to natural systems, where we’re making room for the flood,” Dhalla says.

“We’re opening it up … so we can convey more water and protect the area from flooding.”

Similar naturalization projects are planned to reconfigure rivers in the Vaughan and Brampton city centres.

And across suburbs north of Toronto, the authority has forbidden development on sensitive areas and flood plains, leaving ribbons of green beside many rivers and streams.

Running a flood warning system is also a big part of the mandate, Dhalla says. “We have staff that are on call seven days a week, 365 days a year, (to) monitor conditions.”

The TRCA’s flood monitoring combines streams of data from Environment Canada with a series of 125 rain- and stream-gauging stations across the region. Some 25 of these are equipped to send out real-time data on changes in water levels.

The authority’s operating budget for water risk management was around $670,000 last year, while it spent nearly $27 million in capital endeavours.

Dhalla says long-established centres like areas of the old city of Toronto are particularly vulnerable because tightly compacted infrastructure long made large-scale control measures such as diversion channels and bans on flood-plain development impractical.

“We’re still repairing the erosion from the July (2013) storm event,” Dhalla says.

“So much was lost. People … lost their backyards; houses were at risk of falling in. People were 20 metres away from the river.”

Compounding the risk in dense urban areas is the ubiquitous pavement, which prevents the natural absorption of water into the earth and plants and sends heavy rains, dirtied with pollutants, directly into streams and overburdened storm sewers.

“I’d say over 70 per cent of the urban area in our jurisdiction doesn’t have adequate stormwater controls,” Dhalla says.

Solutions

Heavily urbanized areas do not mix well with rivers and streams. Often built before effective storm management strategies were established, cities dipped down dangerously into flood plains and laid out roadways and parking lots that sent rainwater and melt water rushing into the channels.

“So every single opportunity you can take (to retrofit) highly urban areas you have to,” says Sameer Dhalla of the Toronto and Region Conservation Authority. The associate director in charge of restoration and infrastructure proposes a variety of measures to prevent flooding in the area. They range from simple steps that homeowners or businesses can take such as putting in green roofs to steps involving the TRCA or local governments.

Stormwater Ponds

These take water through collection pipes from urban areas during heavy rains, hold it, and release it slowly into rivers or lakes. The ponds also allow pollutants picked up from pavement to settle as sediments, cleaning the water before it enters the natural system. One such pond was built in North York’s Earl Bales Park.

Green Roofs

The plants and grasses that adorn these rooftop gardens are water absorption machines. They take it up through their roots, use it for photosynthesis and evaporate it back into the air through their leaves in a process known as transpiration. A Toronto bylaw mandates green roofs on many new buildings.

Bioswales

These planted, channelled gullies can be built around parking lots and other paved surfaces where they collect water runoff and use it to feed the foliage. Toronto will be installing these along some rebuilt streets and roadways in the future. Examples are on Bay St. between Grosvenor St. and Wellesley St.

Rain Barrels

Barrels and cisterns placed at homes and businesses collect rain runoff from eaves systems, which owners can then use to water their lawns and plants during dry spells.

Rain Gardens

These are planted in depressions, with foliage that is tolerant of the contaminants in runoff water. The loose soil beneath retains rain longer and filters the water not used by the plants on top. The plants can be fed by eavestrough systems or planted in areas adjacent to high-runoff surfaces.

Permeable pavement may be the most groundbreaking of retrofit proposals. The multilayered system drinks in rainwater and cleans it of the metal-bearing sediments and petroleum pollutants, says Andrea Bradford, a water engineering expert at the University of Guelph.

Most current versions of these products could be used now on parking lots, driveways, shoulders, residential streets or sidewalks, but not on heavily trafficked roads, Bradford says. The cement is being tested now in Mississauga and in the U.S.

On top, the pavements can have familiar interlocking blocks that allow water through the cracks. New permeable concretes and asphalts are being rolled out that contain little if any of the small sandy aggregates, known as fines, abundant in normal mixtures, says Bradford. This leaves gaps between the larger pieces of gravel that allow water to pass through

A thin layer of smaller gravel acts as a smooth bedding for the asphalt or concrete above

A base of larger rock aggregates acts as a reservoir, storing water until it can seep into the ground below. The lower levels of aggregates act as filters for the water as it passes into the earth below and groundwater system. They offer vast storage basins in heavy rains, keeping water away from streams and rivers.

At the bottom is a soil subsurface that has been left uncompacted.

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